Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains vii, 80 p. : ill. (some col.) Vita. Includes abstract. Includes bibliographical references (p. 72-76).

Neutrophil granulocytes constitute the front line of defense in the innate immune response to invading microorganisms, but can also contribute to development of inflammatory disease and tissue destruction following e.g. myocardial infarction or stroke. During inflammatory activation, neutrophils leave the blood, interact with extracellular matrix proteins, and migrate into tissues in response to chemotactic factors to phagocytose and kill infectious agents by using toxic granule contents and reactive oxygen metabolites. The functional neutrophil response relies on exocytosis of cytoplasmic granules, each containing membrane proteins, which are thereby mobilized to the plasma membrane. Specific programmed cell death (apoptotic) pathways regulate neutrophil homeostasis, where an inflammatory milieu can prolong the life span of neutrophils to several days, whereas non-activated neutrophils are committed to constitutive/spontaneous apoptosis within hours. Signal regulatory protein alpha (SIRPα) is a surface glycoprotein with two intracellular immunoreceptor-tyrosine-based inhibitory motifs (ITIMs), which is highly expressed in neutrophils and other myeloid cells. In other cell types, SIRPα has been shown to regulate cellular functions such as cell migration and phagocytosis. The aim of the present thesis was to investigate neutrophil SIRPα expression in response to inflammatory activation or apoptosis, and how this receptor can regulate neutrophil adhesion and cell migration. Neutrophils contain several subcellular granule compartments, including primary (azurophilic), secondary (specific), tertiary (gelatinase) granules, and a fourth compartment called secretory vesicles. In resting neutrophils, SIRPα was found to be present in the plasma membrane and in all types of granules except for the azurophilic granules. Stimulation with the bacterial peptide fMLF in vitro, or inflammatory activation in vivo, was found to rapidly mobilize SIRPα to the neutrophil cell surface. In mice expressing a mutated form of SIRPα, where the cytoplasmic signaling domain was deleted, we found an enhanced accumulation of neutrophils in the peritoneal cavity in a peritonitis model. These findings therefore suggest that an increased amount of SIRPα on the surface of activated neutrophils could serve to negatively fine-tune neutrophil accumulation in inflammation. Neutrophil priming means that the cell becomes partially activated, in a way that facilitates subsequent full activation. One part of the priming process is a moderate exocytosis of granules, mostly the secretory vesicles, which increases the density of certain receptors on the cell surface. It also involves the activation of adhesion receptors called integrins. We found that TNFα-induced priming involved an increased accumulation of SIRPα on the cell surface. When comparing wild-type and SIRPα-mutant neutrophils, we found a strongly reduced TNFα-stimulated and β2 integrin-dependent adhesion of mutant neutrophils to type I collagen or fibrinogen. This adhesion defect resulted in a reduced adhesion-dependent activation of the respiratory burst and an increased chemotactic response of SIRPα-mutant neutrophils in vitro. During neutrophil apoptosis, several receptors are known to be shed from the cell surface (e.g. CD16 and CD43). We found that also SIRPα is shed from the surface during spontaneous as well as Fas-induced apoptosis. The shedding mechanism was found to involve matrix metalloproteinase (MMP) activity, mostly that of MMP-3 and MMP-8. In conclusion, neutrophil cell surface SIRPα expression is regulated during neutrophil activation and seems to play an important role in stimulating β2-integrin-dependent adhesion. This way, SIRPα can negatively fine-tune neutrophil migration and accumulation in inflammation. During apoptosis, SIRPα is shed from the cell surface, which may be one mechanism contributing to the well-known down-regulation in the adhesiveness of apoptotic neutrophils.

Following starvation, Dictyostelium discoideum cells aggregate, a response that requires chemotaxis to cyclic AMP (cAMP) and the relay of the cAMP signal by the activation of adenylyl cyclase (ACA). Insertional inactivation of the rasG gene resulted in delayed aggregation and a partial inhibition of early gene expression, suggesting that RasG does have a role in early development. When the responses of rasG⁻ cells to cAMP were compared with the responses of rasC⁻ strain, these studies revealed that signal transduction through RasG is more important in chemotaxis and early gene expression, but that signal transduction through RasC is more important in ACA activation. Characterization of a rasC⁻/rasG⁻ mutant revealed that both cAMP chemotaxis and adenylyl cyclase (ACA) activation were negligible in this strain. The ectopic expression of carA from the actin 15 promoter restored early developmental gene expression to the rasC⁻/rasG⁻ strain, rendering it suitable for an analysis of cAMP signal transduction. Since there was negligible signaling through either the cAMP chemotactic pathway or the adenylyl cyclase activation pathway in this strain, it is clear that RasG and RasC are the only two Ras subfamily proteins that directly control these pathways. The mutational analysis of Switch I and Switch II regions also defined the key residues that generate functional differences between RasC and RasG. Rap1 is also activated in response to cAMP but its position in the signal transduction cascade was clarified by the finding that its activation was totally abolished in rasC⁻/rasG⁻/[act15]:carA and in rasG⁻ cells, but only slightly reduced in rasC⁻ cells. The finding that in vitro guanylyl cyclase activation is also abolished in the rasC/rasG⁻4act15]:carA strain identifies RasG⁻/RasC⁻ as the presumptive monomeric GTPases required for this activation. The phenotypes of the vegetative ras null mutants were also examined. The results indicate that RasG plays an important role in cytokinesis. The partial absence of chemotaxis to folate in rase cells compared to the total absence of chemotaxis to folate in rasC⁻/rasG⁻, and rasC⁻/rasG⁻/[act15]:carA cells suggests a compensatory role of RasC for RasG during this process, a similar phenomenon to that observed for cAMP chemotaxis by aggregating cells.

Following starvation, Dictyostelium discoideum cells aggregate, a response that requires chemotaxis to cyclic AMP (cAMP) and the relay of the cAMP signal by the activation of adenylyl cyclase (ACA). Insertional inactivation of the rasG gene resulted in delayed aggregation and a partial inhibition of early gene expression, suggesting that RasG does have a role in early development. When the responses of rasG⁻ cells to cAMP were compared with the responses of rasC⁻ strain, these studies revealed that signal transduction through RasG is more important in chemotaxis and early gene expression, but that signal transduction through RasC is more important in ACA activation. Characterization of a rasC⁻/rasG⁻ mutant revealed that both cAMP chemotaxis and adenylyl cyclase (ACA) activation were negligible in this strain. The ectopic expression of carA from the actin 15 promoter restored early developmental gene expression to the rasC⁻/rasG⁻ strain, rendering it suitable for an analysis of cAMP signal transduction. Since there was negligible signaling through either the cAMP chemotactic pathway or the adenylyl cyclase activation pathway in this strain, it is clear that RasG and RasC are the only two Ras subfamily proteins that directly control these pathways. The mutational analysis of Switch I and Switch II regions also defined the key residues that generate functional differences between RasC and RasG. Rap1 is also activated in response to cAMP but its position in the signal transduction cascade was clarified by the finding that its activation was totally abolished in rasC⁻/rasG⁻/[act15]:carA and in rasG⁻ cells, but only slightly reduced in rasC⁻ cells. The finding that in vitro guanylyl cyclase activation is also abolished in the rasC/rasG⁻4act15]:carA strain identifies RasG⁻/RasC⁻ as the presumptive monomeric GTPases required for this activation. The phenotypes of the vegetative ras null mutants were also examined. The results indicate that RasG plays an important role in cytokinesis. The partial absence of chemotaxis to folate in rase cells compared to the total absence of chemotaxis to folate in rasC⁻/rasG⁻, and rasC⁻/rasG⁻/[act15]:carA cells suggests a compensatory role of RasC for RasG during this process, a similar phenomenon to that observed for cAMP chemotaxis by aggregating cells.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 140-161). Also available in electronic version.

Ulm, Univ. Diss., 2006.

Konstanz, Univ., Diss., 2008.

Thesis (Ph. D.)--Virginia Commonwealth University, 2007. / Prepared for: Dept. of Microbiology and Immunology. Bibliography: leaves 92-108. Also available online via the Internet.

Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 42-47). Also available on the World Wide Web.

München, Techn. Univ., Diss., 2004.